1. Field of the Invention
The present invention relates to an observation apparatus of a video system and, more particularly, to an observation apparatus suitable for fluorescent observation.
2. Description of the Prior Art
An observation apparatus of a video system reproduces the image of an object taken by an image pickup device on a reproducing monitor for observation. The image pickup device is provided with a small built-in video camera unit employing a solid state image pickup element, such as a CCD, and an illuminating system capable of illuminating the object with intense illuminating light. The observation apparatus enables the observation of a magnified image of the object illuminated with the illuminating light emitted by the illuminating system. Such a known observation apparatus is disclosed, for example, in Japanese Patent Publication No. 20615/92.
This known observation apparatus enables the observation of the object in various modes of observation by illuminating the object in various modes of illumination. A fluorescent observation mode is one of the various modes of observation. In a fluorescent observation mode, the object is illuminated with illuminating light selected among visible light in a specified wavelength region, such as a red light wavelength region, a green light wavelength region or a blue light wavelength region, and ultraviolet light, to relieve a fluorescent composite or a fluorescent structure that is excited specifically for luminescence by the illuminating light to emit fluorescent light for observation.
FIG. 3 shows an example of a known observation apparatus that enables fluorescent observation. This known observation apparatus is provided with an image pickup device 1 having an illuminating system which transmits light emitted by an external illuminating lamp 2 through an optical fiber bundle 3. The light emitting ends of time optical fibers 3f of the optical fiber bundle 3 are arranged in a circular arrangement, and the illuminating light emitted through the illuminating ends is condensed in an observation field by a semispherical condensing light guide 4.
The image pickup system of the observation apparatus comprises a camera unit 5 and an optical unit 6 for focusing the image of an object M on the image pickup device 5e of the camera unit 5. The illuminating system is provided with a first filter 7 for wavelength selection to pass light of a wavelength in a specified wavelength region, and the optical unit 6 is provided with a second filter 8 for region rejection to absorb the light passed through the first filter 7. The image taken by the image pickup device 1 is displayed on a monitor 9 for observation.
In this observation apparatus, the second filter 8 absorbs the illuminating light reflected by the object M and passes only fluorescent light emitted by a fluorescent composite or a fluorescent structure in the object made luminous by excitation with the illuminating light so that only the fluorescent light falls on the image pickup system for luminescent observation.
Accordingly, when using this known observation apparatus for fluorescent observation, the types of objects which can be observed are dependent on the combination of the first filter 7 and the second filter 8, and the filters 7 and 8 must be changed for other filters when observing another object or a fluorescent composite having another characteristics in the object.
Problems arises when changing the filters, particularly, the second filter. Since the second filter is disposed within the image pickup device having a small space available, it is difficult to design a mechanism for holding the second filter and it requires troublesome work to change the second filter for another filter.
Furthermore, the second filter must be capable of being set for both ordinary observation and fluorescent observation. Fluorescent observation is particularly useful when used in combination with ordinary observation. To enable the observation apparatus both ordinary observation and fluorescent observation, the second filter needs to be removed from the image pickup device or moved away from the path of the image light for luminescent observation. Both removing the second filter from the image pickup device and moving the second filter away from the path of the image light need mechanisms which are difficult to design.
When light in the ultraviolet region, i.e., ultraviolet radiation, is used as illuminating light for fluorescent observation, basically, the illuminating light reflected by the object need not be eliminated, and hence, there is no significant problem attributable to the second filter. However, if the illuminating light reflected by the object is not eliminated, the clearness of the fluorescent image is spoiled. As mentioned above, the image pickup device 1 of the observation apparatus of a video system can be held by hand and can be brought into contact with or near the object for observation. Although such a method of observation has a great advantage that the degree of freedom of observation is very large as compared with that of the conventional microscope employing a stationary stand for supporting the object, it is difficult to provide the image pickup device with a screening means for effectively screening the object from external light when ultraviolet radiation is used for fluorescent observation; consequently, the contrast of the image is reduced by undesired external light, i.e., disturbing light, to spoil the clearness of the fluorescent image.